plus Im not sure if modo if a 2.5 3d rendering program, so Im not sure if you could sculpt with such massive amounts of polies like you can with zbrush. Personally If I had $700 to blow on 3d modeling I'd get zbrush, Blender, Photoshop and any importers/exporter you might need for your pipeline.
How should that work? Adobe Photoshop CS3 alone takes 649 $ away from your budget:
http://www.adobe.com/products/photoshop/photoshop/But if you replace PS with GIMP then it works fine. You only have to pay for ZBrush (595 $) and you get the rest of them for free (Blender and GIMP) plus a few additional smaller tools of your choice like Fragmotion, Milkshape or a terrain editing software like this one:
http://www.freeworld3d.org/At Dexsoft we are working alot with GIMP and some of our packs have been made with Blender (like the last and the upcoming vegetation pack).
